Search Results (2)

In this paper, a comprehensive analysis of the combined effect of major influencing parameters on heat transfer in a single U-tube BHE (sBHE) and a double U-tube BHE (dBHE) with two independent circuits was performed by using a validated numerical heat transfer model. Geometrical parameters, such as shank spacing (with maximum, average, and minimum values), borehole diameter (large, medium, and small borehole sizes), and borehole depth (shallow, average, and deep borehole depths) as well as the thermal conductivity of soil and grout, which ranges from minimum to high values, were considered. The combined impact of these parameters was included under the following four major cases: (1) the combined effect of borehole depth, borehole size, and shank spacing; (2) the combined effect of borehole depth and soil and grout thermal conductivity; (3) the combined effect of soil and grout thermal conductivity and borehole size; and (4) the combined effect of soil thermal conductivity, borehole size, and shank spacing. Each of these major cases has nine different design options for both sBHEs and dBHEs. A series of results of heat transfer per unit borehole depth were generated for all the considered various cases. With the given parameters, the BHE case that provides the highest heat transfer among the various cases of sBHEs and dBHEs were obtained. Full article

In the last decade, due to climate change concerns and new environmental regulations in the EU, there was a tremendous rise in installed heat pump systems in new homes and buildings. The majority of these installed units are related to air-source heat pumps, as they offer a good trade-off between capital and operating expenses. However, when analysing heating and cooling heat pump systems from the primary energy consumption and ecological aspects, groundwater and shallow geothermal heat pump systems offer superior efficiency, compared to all market-available thermo-technical systems today. In the last decade, ground-source systems have seen some technological improvement by employing new borehole heat exchanger designs, such as piping with internal fins and a wider diameter (so called Turbocollector) to enhance the heat transfer between fluid and rock, as well as to reduce the pressure drop in the system. Furthermore, the process of drilling deeper offers higher ground temperatures and consequently higher seasonal performance factors in the heating cycle, due to the effect of the geothermal gradient. Nevertheless, although deeper boreholes provide better heat extraction rates per meter during the heat pump heating cycle, at the same time, it reduces heat rejection rates during the heat pump cooling cycle. The objective of this paper is to analyse and evaluate benefits and downsides of a new approach in the heat pump system design with deeper borehole heat exchangers of up to 300 m, comparing it to the traditional design of double-loop exchangers with 100 m depth. The geothermal borehole grid design simulation model, along with heat extraction and rejection, is performed on a yearly basis. The results are showing that the benefits of shallow geothermal boreholes, from the hydraulic and thermodynamic point of view, still dominate over deeper solutions. Full article